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Quantum spin simulators in diamond

Periodic Reporting for period 2 - Q-DIM-SIM (Quantum spin simulators in diamond)

Reporting period: 2018-07-01 to 2019-12-31

The project's ultimate goal is to construct a quantum simulator based on localized, atomic-sized defects in diamond called NV (nitrogen-vacancy) centers. While it may sound abstract, this goal dates back nearly 40 years, when Richard Feynman realized that in order to understand the intricacies of Nature, which is governed by quantum physics, we need a quantum simulator (as opposed to a classical one). A huge class of unsovled problems in physics could be addressed using a quantum simulator, such as the mechanism for high-temperature superconductivity and magnetism in two-dimensional systems, potentially leading to revolutionary applications - zero-loss electrical transmission lines rendering all current energy issues irrelevant, and novel magnetic based computers and memories. Over the years significant progress has been made in attempting to realize such quantum simulators in a variety of physical systems with promising results, although their applicability is still limited.

Here we focus on a completely new platform for realizing a quantum simulator, namely NV centers in diamond. The degree of control and coherence of these solid-state defects, and their inherent physical properties as quantum spins, make them particularly suitable for simulating important spin-based problems, and thus potentially provide profound impact on real-world applications. The developments addressed within this proposal could have additional repercussions on other quantum technologies, such as quantum sensors and quantum networks, and might provide a crucial stepping stone for realizing a general quantum computer.

The project objectives aim at realizing its ultimate goal, by advancing the state-of-the-art in several directions: we will improve the NV quantum properties, i.e. their coherence; we will develop new techniques to create diamond samples with optimized NV concentrations; we will enhance the measurement fidelity of the NV's quantum state; we will realize an optical super-resolution microscope to address single NVs at the nanoscale; we will couple NVs through specifically designed superconducting structures, which channel magnetic fields from one NV to the other; we will develop and apply advanced control techniques, to enable desired quantum simulations using the combined platform.

This ambitious project introduces ground-breaking concepts and paradigms, develops new approaches and techniques, aiming at establishing a novel platform for quantum simuation of long-standing problems with the prospect of revoluionary impact on real-world applications. Moreover, these developments stand to critically advance other quantum technologies, and potentially lead in the future to general quantum computation.
- We have studied theoretically (analytically and numerically) the coupling of NVs using superconducting structures, optimizing the coupler parameters in order to identify the different dependencies and sensitivities, and to achieve a better understanding of the underlying physics.
- We have established the nano-fabrication process required for e-beam lithography of the desired structures on diamond, and created diamond substrates with structured Niobium thin films on top.
- We have established the nano-fabrication process for creating structures in diamond using focused ion beam (FIB), and demonstrated the creation of nano-pillars in relevant diamond samples.
- We have developed and demonstrated advanced schemes for spin manipulation and characterization, specifically a novel noise spectroscopy scheme based on continuous modulation (denoted as DYSCO), and a hyper-polarization scheme enhancing the performance of NOVEL (denoted as refocused NOVEL, or rNOVEL).
- We have optimized schemes for NV coherence enhancement along with the creation of high-concentration ensembles, using a combination of dynamical decoupling approaches and electron irradiation. This is required for reaching the interaction dominated regime in NV ensembles.
- We have developed novel Hamiltonian engineering methods, extending previous capabilities and enabling the simulation of previously unattainable dynamics.
- We have developed new techniques for reading out the NV quantum state, based on sophisticated nano-photonic structures and optical illumination schemes.
As stated in the section above, the following progress beyond the state-of-the-art has been achieved:

- Advanced noise spectroscopy scheme based on the NOVEL sequence.
- Enhanced hyper-polarization scheme improving the capabilities of NOVEL in the presence of noise (denoted as rNOVEL).
- Record long coherence times for NV ensembles using advanced dynamical decoupling approaches at low temperatures.
- Enhanced NV concentrations using electron irradiation in order to retain useful coherence properties.
- Develop fabrication process for superconducting structures on a diamond substrate.
- Develop improved quantum state readout schemes.
- Analyze in-detail magnetic coupling through superconducting structures using advanced analytical, theoretical tools.
- Devise novel Hamiltonian engineering approach, extending the state-of-the-art and leading to completely new capabilities.
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